Exploring India’s genetic history

What: Following up on a 2009 study that traced the genetic heritage of nearly all modern Indian groups to two distinct ancestral populations, Broad researchers and their Indian colleagues analyzed genomic data from across present-day India and found that most of India’s population mixture occurred 1,900 to 4,200 years ago.

“This genetic data tells us a three-part cultural and historical story,” said David Reich, a senior associate member at the Broad who was one of the leaders of the study. “Prior to about 4,200 years ago there was no mixture. After that, widespread mixture affected almost every group in India. And finally, in the last 1,900 years, mixture stopped and everything has frozen in place.”

The researchers suspect this recent shift resulted from endogamy – the practice of marrying only within one’s class or ethnic group – suggesting that India’s caste system developed relatively recently.

Who: An international team from the Broad Institute, Harvard Medical School, and CSIR-Centre for Cellular and Molecular Biology in Hyderabad, India. Broad researchers included David Reich (co-senior author), Priya Moorjani (co-first author), Nick Patterson, and Bonnie Berger.

Why: Reich’s lab is part of the Broad’s Program in Medical and Population Genetics (MPG), which seeks to understand how genomic variation – including variation within and across populations – impacts human health. Knowledge about human population history – including evolutionary history and patterns of genetic variation – can help inform future studies in medical genetics.

Where to find it: The American Journal of Human Genetics